Getting to the Truth About the Effectiveness of Masks in Preventing COVID-19
Authors: Christine Laine, Stephanie Chang
Journal: Annals of Internal Medicine (2023)

Editorials16 May 2023Getting to the Truth About the Effectiveness of Masks in Preventing COVID-19FREEChristine Laine, MD, MPH, and Stephanie Chang, MD, MPHChristine Laine, MD, MPHEditor in Chief, Annals of Internal Medicine, and American College of Physicians, Philadelphia, PennsylvaniaSearch for more papers by this author, and Stephanie Chang, MD, MPHDeputy Editor, Annals of Internal Medicine, and American College of Physicians, Washington, DCSearch for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/M23-1120 SectionsAboutVisual AbstractPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinkedInRedditEmail Before the COVID-19 pandemic, medical masks were just devices worn with the aim of preventing respiratory infection. During the pandemic, masking recommendations differed widely and changed rapidly across settings, and masks became a controversial political symbol. Laboratory studies that examined the physical properties of masks abounded but were generally small, often involved robotic mask wearers, and examined the spread of particles rather than the spread of infection. Some (but not all) observational studies comparing communities with and without prevalent masking suggested an association of masking with less COVID-19, but it is challenging for such studies to disentangle whether findings were due to masks, to unmeasured confounding, or to concomitant physical distancing and other measures. There are only 3 published trials examining the effectiveness of various masking interventions to reduce SARS-CoV-2 infection in real-world settings—2 in community settings (1, 2) and 1 in hospitals (3). Although trials provide the highest quality of evidence, the evolving pandemic with changes in natural immunity, vaccination availability, and different virus variants presented substantial challenges to arriving at definitive answers to the question about the effectiveness of masks in preventing SARS-CoV-2 infection (4).In their article, Chou and Dana report the final update of a living systematic review that attempts to answer this question (5). They identified the 3 randomized trials cited earlier and 21 observational studies that controlled for confounders (7 in community and 4 in patient care settings) that examined risk for SARS-CoV-2 infection. They conclude that mask interventions may be associated with a small reduction in risk for SARS-CoV-2 infection in community settings and that risk for infection in patient care settings seems similar with surgical masks and N95 respirators. Substantial caveats accompany both conclusions. Chou and Dana’s review differed from a recently published Cochrane review (6) in that it focused on studies examining masking interventions and SARS-CoV-2, whereas the Cochrane review examined studies of various physical interventions, including masks, to reduce viral respiratory illness in general. Chou and Dana examined evidence published through 2 January 2023 and provided qualitative results, whereas the Cochrane group examined evidence through October 2022 and provided quantitative estimates. The Cochrane review reported with moderate certainty that wearing masks in the community probably makes little or no difference in the transmission of influenza-like or COVID-19–like illness (risk ratio, 0.95 [95% CI, 0.84 to 1.09]) and were very uncertain that there was any difference between N95 respirators and medical or surgical masks in preventing the spread of viral respiratory illness. Both reviews identified a lack of evidence examining potential harms associated with masking interventions.Both reviews are careful, systematic examinations of the current state of evidence for the effectiveness of masking interventions in preventing COVID-19 that suggest a substantial amount of uncertainty and identify important evidence gaps. Yet, some people state with certainty that masking is effective, and others state with equal certainty that it is not. How do we get at the truth?First, we must clarify that people are talking about the same thing. Are people referring to the effectiveness of a mask to prevent passage of virus or to prevent SARS-CoV-2 infection? Are they referring to the effectiveness of masks themselves or of masking recommendations or policies? Certainty that masks are effective may rely on studies of viral penetration, whereas certainty of mask ineffectiveness may rely on studies of masking recommendations. Second, we must consider masking as 1 element of multicomponent strategies to reduce transmission of infection and how accompanying strategies may affect mask effectiveness. Third, we need to be explicit in weighing benefits and harms. Although some may consider any evidence of benefit sufficient to justify masking, others believe that inconvenience, discomfort, or communication impedance outweigh small benefits. Policymakers making masking recommendations and establishing policy should use structured evidence to decision frameworks that clearly acknowledge and consider uncertainty and balance benefits and harms (7).As we emerge from COVID-19 being a public health emergency, we must acknowledge the inevitability of future viral epidemics and to reflect on the types of studies that could better inform us about the effectiveness of masking interventions. Randomized trials of masking interventions are challenging and demand pragmatism, but existing trials show that they are feasible. To know whether masks are effective, we need to examine them in real-world situations. A mask may block virus in a laboratory, but that doesn’t tell us how masks function when worn by real people in real-world settings. A mask that is more permeable to virus may function better than one that is impermeable to virus if the more permeable mask is easier to wear properly and consistently. Masks are recommended to prevent transmission of infection, so studies should examine clinically meaningful infection outcomes. Interpretation of study results demands a priori definition of clinically meaningful differences so that even when CIs cross 1, the degree to which the observed outcomes are compatible with meaningful differences can be assessed. Mask recommendations occur in the context of other infection control measures, infection prevalence, and vaccination rates. Studies of masking, whether observational or interventional, must recognize and account for these concomitant measures and contextual factors (8, 9). Alternative study designs, such as process evaluation trials or realist trials may inform what conditions are necessary for masking to work in practice. Finally, studies should systematically assess potential harms so that benefits, especially if small or uncertain, can be balanced against harms.There is evidence that masks could work to prevent COVID-19, but substantial gaps remain about whether they do work and under what conditions. In the face of future viral outbreaks, we must move quickly to fill the gaps with timely studies that avoid the limitations of studies done to date. We may never reach definitive truth about when the benefit of masking interventions outweighs the harms, but it is imperative that we design studies that fill information gaps, interpret the evidence accurately, and are honest about what we do and do not know with certainty when making decisions and setting policy about masking.References1. Abaluck J, Kwong LH, Styczynski A, et al. Impact of community masking on COVID-19: a cluster-randomized trial in Bangladesh. Science. 2022;375:eabi9069. [PMID: 34855513] doi:10.1126/science.abi9069 CrossrefMedlineGoogle Scholar2. Bundgaard H, Bundgaard JS, Raaschou-Pedersen DET, et al. Effectiveness of adding a mask recommendation to other public health measures to prevent SARS-CoV-2 infection in Danish mask wearers. A randomized controlled trial. Ann Intern Med. 2021;174:335-343. [PMID: 33205991] doi:10.7326/M20-6817 LinkGoogle Scholar3. Loeb M, Bartholomew A, Hashmi M, et al. Medical masks versus N95 respirators for preventing COVID-19 among health care workers. A randomized trial. Ann Intern Med. 2022;175:1629-1638. [PMID: 36442064] doi:10.7326/M22-1966 LinkGoogle Scholar4. Laine C, Goodman SN, Guallar E. The role of masks in mitigating the SARS-CoV-2 pandemic: another piece of the puzzle. Ann Intern Med. 2021;174:419-420. [PMID: 33205993] doi:10.7326/M20-7448 LinkGoogle Scholar5. Chou R, Dana T. Major update: masks for prevention of SARS-CoV-2 in health care and community settings—final update of a living, rapid review. Ann Intern Med. 2023;176:827-835. doi:10.7326/M23-0570 LinkGoogle Scholar6. Jefferson T, Dooley L, Ferroni E, et al. Physical interventions to interrupt or reduce the spread of respiratory viruses. Cochrane Database Syst Rev. 2023;1:CD006207. [PMID: 36715243] doi:10.1002/14651858.CD006207.pub6 CrossrefMedlineGoogle Scholar7. Alonso-Coello P, Schünemann HJ, Moberg J, et al ; GRADE Working Group . GRADE evidence to decision (EtD) frameworks: a systematic and transparent approach to making well informed healthcare choices. 1: Introduction. BMJ. 2016;353:i2016. [PMID: 27353417] doi:10.1136/bmj.i2016 CrossrefMedlineGoogle Scholar8. Campbell NC, Murray E, Darbyshire J, et al. Designing and evaluating complex interventions to improve health care. BMJ. 2007;334:455-459. [PMID: 17332585] CrossrefMedlineGoogle Scholar9. Minary L, Trompette J, Kivits J, et al. Which design to evaluate complex interventions? Toward a methodological framework through a systematic review. BMC Med Res Methodol. 2019;19:92. [PMID: 31064323] doi:10.1186/s12874-019-0736-6 CrossrefMedlineGoogle Scholar Comments0 CommentsSign In to Submit A Comment Jose Fernando Feurtes-BucheliUniversidad Icesi, Facultad de Ciencias de la Salud16 May 2023 Consider the epidemiological situation and closely monitor the behavior of infectious diseases in response to changes in public health measures I found your observation remarkably interesting, and I agree with most aspects. I consider it of utmost importance to consider the context in which studies are conducted to address the research question, especially due to the significant, complex, and difficult-to-control biases that can arise in studies conducted during pandemics, where changes can occur hastily. I would like to comment on a study carried out in Colombia during a well-defined epidemiological moment (1). Although this study was observational, the authors considered several relevant aspects of the epidemiological situation in which two public health measures regarding the use of masks were modified. They managed to report interesting results that led to the conclusion, on the one hand, which considering the epidemiological moment is crucial, and on the other hand, that close surveillance of the behavior of pandemic infectious diseases at the local level is required to guide public health recommendations based on changes in epidemiological patterns. All the above leads me to emphasize that evidence-based recommendations should be adapted to the local context, considering risks, benefits, and necessity. Thank you for considering my comments. References: Fuertes-Bucheli JF, Peláez-Martínez JD, Martínez-Niño M del M, Aguilar-Gonzalez AM, Dorris M, Ferro BE, Pacheco R. Quinta arremetida de COVID-19 y el uso de mascarillas en espacios abiertos y cerrados. Univ. Salud. 30 de agosto de 2022;24(3):267-72. DOI: https://doi.org/10.22267/rus.222403.281 Susanne DavidsonUHI24 May 2023 How can any study design ever account for the many factors outside the setting? Unless study participants would live in a kind of "vaccuum" without any social contacts where masks in most cases will not be worn (at home with family members who have outside contacts of their own), I personally cannot see any study design that could exclude such factors. How can robust evidence be generated, if compliance, correct wearing (for example shaving off a beard, etc.), personal behaviour, family, and work settings can hardly be controlled? Based on very personal experiences with a family member who underwent weeks of chemotherapy and associated travel (during times of high community and nosocomial transmission) whilst meticulously sticking to FFP3 masks in all indoor settings and at all times (with the result of not being infected), I would propose to include individual case studies in study design about the efficacy of masks in preventing infections. Such an approach could potentially mitigate confounding factors, support easier evaluation of compliance and could generate meaningful results. Author, Article, and Disclosure InformationAuthors: Christine Laine, MD, MPH; Stephanie Chang, MD, MPHAffiliations: Editor in Chief, Annals of Internal Medicine, and American College of Physicians, Philadelphia, PennsylvaniaDeputy Editor, Annals of Internal Medicine, and American College of Physicians, Washington, DCDisclosures: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M23-1120.Corresponding Author: Christine Laine, MD, MPH, American College of Physicians, 190 N. Independence Mall West, Philadelphia, PA 19106; e-mail, claine@acponline.org.This article was published at Annals.org on 16 May 2023. PreviousarticleNextarticle Advertisement FiguresReferencesRelatedDetails Metrics June 2023Volume 176, Issue 6Page: 870-871KeywordsCOVID-19Prevention, policy, and public healthPulmonary diseasesRespiratorsViral transmission and infection ePublished: 16 May 2023 Issue Published: June 2023 Copyright & PermissionsCopyright © 2023 by American College of Physicians. All Rights Reserved.PDF downloadLoading ...